File system including non-volatile semiconductor memory device having a plurality of banks

Abstract

A flash memory includes a data bank having a plurality of banks, a merge bank, and an update data bank. A file system using the flash memory includes a unit storing update data corresponding to a data rewrite command into the update data bank, a unit selecting the latest update data for each block from update data stored in the update data bank when the update data bank becomes full, and a processing unit processing the latest update data. The processing unit includes a unit storing latest update data into a merge bank, a unit selecting data associated with the latest update data from the data bank to store the selected data into the merge bank, and a unit setting the merge bank as a new data bank.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to a file system of a computer system, and particularly to a file system using a non-volatile semiconductor memory device such as a flash memory or the like.2. Description of the Related ArtA flash memory is a type of an EEPROM (Electrically Erasable and Programmable ROM) which can be rewritten electrically, and has such characteristics that it is less expensive than a DRAM (Dynamic Random Access Memory), a backup power supply is unnecessary, the change of bits is irreversible, data is erased bank by bank, erasure of a bank requires time, and the number of bank erasures is limited.The flash memory having such characteristics is widely used as a data storage device in equipment such as a mobile phone, a PDA (Personal Digital Assistant), a digital still camera and the like. In such equipment, varieties of data to be stored have increased, leading to frequent operations such as saving, deleting and moving...

AI Technical Summary

Benefits of technology

An object of the present invention is to provide a file system including a non-volatile semiconductor memory device, which can be executed at high speed.

Another object of the present invention is to provide a file system including a non-volatile semiconductor memory device, which has a long operation life.

A further object of the present invention is to provide a file system including a non-volatile semiconductor memory device, which can back up data even if unexpected power shut-off occur.

A yet further object of the present invention is to provide a file system including a non-volatile semiconductor memory device, which has a long operation life by averaging the number of erasures for each bank in the non-volatile semiconductor memory device.

A still further object of the present invention is to provide a file system including a non-volatile semiconductor memory device, which has a long operation life by making the number of bank erasures as small as possible in the non-volatile semiconductor memory device.

Problems solved by technology

This raises a problem as described below when a file system is constructed on the flash memory.

Thus, in order to update five file blocks, banks must be erased five times. As described earlier, a large amount of time is required for such erasure by the bank, and there is a certain limit for the number of erasures.

However, in the conventional file system, bank erasure frequently occurs, lowering operation speed and shortening lifetime of the flash memory.

Moreover, in the conventional file system, if the power is shut off or reset with unexpected timing, the entire file system may be destroyed and hence become unworkable without reformat.

If this happens, the stored data will be lost.

Images